1. Introduction
This invention relates to medical devices, and more particularly to catheters for delivering medical devices.
2. Discussion
Stents are a type of medical device that has been used with great success to treat various conditions of patients, including narrowing or blockage of a blood vessel or other body passage. Generally, stents are often formed as cylindrical mesh tubes which expand from an initial configuration to a deployed shape. In the deployed shape, they act as scaffolding to hold open a body passage or lumen, such as an artery.
Stents have so far been provided in two broad categories, balloon-expandable and self-expanding. Balloon-expandable stents are crimped around a deflated balloon of a balloon catheter, delivered to a desired site for treatment, and forcibly expanded by inflating the balloon to a certain pressure to the deployed shape.
On the other hand, self-expanding stents are compressed to a small initial size and then surrounded by a tube or sheath. Accordingly, self-expanding stent delivery systems do not need a balloon of any kind, resulting in a system fewer components. Once the self-expanding stent is positioned within a desired site for treatment where it is to be implanted, the sheath is withdrawn slightly and pulled from around the stent, while at the same time the stent is held in the desired position. When the stent is uncovered, it tends to automatically and resiliently expand to the desired deployed shape.
With such an arrangement, there may be some amount of initial friction between the sheath and the stent that may occur during stent deployment. Also, a stent that has greater length may tend to generate greater friction.
Accordingly, it is an object of the present invention to provide a delivery system for self-expanding stents which minimizes friction during deployment of the stent.
In addition, it is possible to provide stents with one or more coatings. Such coatings may be of various types, including medicated or therapeutic coatings, lubricious coatings, etc. Of course, it is also desirable to minimize even a remote possibility of damage to a coating during deployment of a coated stent.
An example embodiment of a catheter made according to the principles of the present invention includes a long flexible shaft, a proximal hub assembly, and a specially shaped balloon.
The shaft has an inner body and an outer body. At least the outer body is tubular and surrounds at least a portion of the inner body. The inner body may be tubular as well, and if so, it defines a guidewire lumen.
The term “tubular” is used in its broadest sense; to encompass any structure arranged a radial distance around a longitudinal axis. Accordingly, tubular includes any structure that (i) is cylindrical or not, such as for example an elliptical or polygonal cross-section, or any other regular or irregular cross-section; (ii) has a different or changing cross-section along its length; (iii) is arranged arowid a straight, curving, bent or discontinuous longitudinal axis; (iv) has an imperforate surface, or a periodic or other perforate, irregular or gapped surface or cross-section; (v) is spaced uniformly or irregularly, including being spaced varying radial distances from the longitudinal axis; (vi) has any desired combination of length or cross-sectional size.
The relative positions of the inner and outer bodies can be adjusted by moving them axially or longitudinally with respect to each other.
The balloon is generally cylindrical, and includes an inner and outer balloon portion. The inner and outer balloon portions are affixed to the inner and outer shaft bodies respectively. The area where they are joined is called the inner and outer proximal shoulder of the balloon, respectively. The inner and outer balloon portions extend distally from these proximal shoulders, and meet at a distal leading edge fold. The entire balloon surrounds a stent in an initial configuration, compressing the stent and holding it in place.
According to the unique arrangement of the present invention, the distal area of the balloon has a novel shape, in that the distal section of both the inner and outer balloon portions are both tapered inward. This feature tends to protect the leading distal end of the stent, and also provides for easier advancement of the catheter system along the desired passage for treatment.
The outer hub defines an inflation port connected to the inner tube. An adjustable seal is interposed between the outer hub and the inner body tube. When tightened, the seal secures the inner body tube in a selected position relative to the outer body tube. When the seal is adjusted to a release position, the inner body tube and the outer body tube lumen tube may be moved axially relatively to adjust the effective length of the balloon between its retracted and extended positions. Indicia on the guide wire tube indicate to the physician the relative spacing of the balloon inner and outer shoulders.
Where the stent is surrounded by a deflated balloon, the balloon is advanced into the vessel to be treated until it is within a stenosis to be treated. The inner body tube is then held stationary while the outer body tube is withdrawn to peel the balloon from the stent. Thus, the balloon will be peeled gradually from the stent from the distal to the proximal end of the stent, and allowing the stent to expand and thereby become implanted at a desired location.
Thereafter, if desired, the catheter is may be moved a short distance to position the balloon within the stent, and the balloon may be inflated to assure full stent expansion. The catheter is then removed from the patient being treated.
Accordingly, an object of the present invention is to provide a novel and improved balloon catheter stent delivery system, and processes of utilizing such a catheter for expanding stenoses, opening occlusions, as well as protecting and implanting stents to diseased vessel wall segments.